Physiological responses of men and women to humid and dry heat

Abstract

Sex-related differences were evaluated in 10 males and 9 females under hot-wet and hot-dry conditions. Preacclimatized subjects were exposed to a comfortable climate (20.degree. C, 40% RH) [relative humdity], mild-wet weather (32.degree. C, 80% RH), 2 hot-wet conditions (35.degree. C, 90% RH; 37.degree. C, 80% RH), and 2 hot-dry conditions (49.degree. C, 20.degree. RH; 54.degree. C, 10% RH). Exposures lasted 120 min: 10 min rest, 50 min walk (1.34 m/s), 10 min rest, 50 min walk. During hot-dry exposures, heart rate (HR) and rectal temperature (Tre) were significantly lower for males than females by 13 and 20 beats/min and by 0.25 and 0.32.degree. C for the 2 conditions, respectively, no significant differences in sweat loss (.ovrhdot.msw) were observed. During hot-wet exposures, both mean final Tre and .ovrhdot.msw were lower in females than males by 0.34 and 0.24.degree. C and by 106 and 159 g.cntdot.m-2.cntdot.h-1, respectively (males sweated 25 and 40% more than females). None of these differences correlated with maximal O2 uptake, body weight, skin surface area, or percentage of body fat. During hot-wet exposures, a negative relationship between surface area-to-mass ratio (Ad/wt) and Tre, mean skin temperature, HR and change in heat storage was found. Three major factors are probably involved in these differences: higher AD/wt for females than for males, better sweat suppression from skin wettedness for women, and higher thermoregulatory set point for women than for men.